Patent Document 1, WO01/73832A1 proposed by the present applicants, discloses a batch-type dry etching method having superior productivity to the single wafer treatment. Its essence resides in that Si wafers are vertically arranged in a reaction vessel which is held at 50° C. or less and are rotated, while an etching reactive gas, such as NF3, NH3, H2 or N2 is horizontally fed thereto from a chamber having higher pressure than the reaction vessel, and then the Si wafers are heated to 100° C. or more for the hydrogen termination.
In the batch-type dry etching apparatus of Patent Document 1, lamp heaters radiate heat through a quartz window into the reaction vessel. Since the quartz reacts with the fluoride complex and results in formation of particles, the lamp heaters of an operating apparatus are located on the gas-exhausting side. In addition, the aluminum inner surface of the reaction vessel is subjected to luster treatment, so that the radiation heat is uniformly reflected from the inner lustrous surface of the reaction vessel over the reaction vessel interior. Temperature uniformity is thus enhanced.
When the batch treatment is performed repeatedly by the method of Patent Document 1, the following processes are carried out. That is, Si wafers are introduced in a reaction vessel. Since the interior of a reaction vessel is usually kept under vacuum, when the vessel is not operated, the reaction vessel is temporarily reverted to atmospheric pressure, prior to the introduction of Si wafers into the reaction vessel in the first batch. After introduction of the Si wafers, vacuum evacuation is carried out, and then purge gas such as nitrogen gas is introduced. In the second and subsequent batch treatments, when the wafer temperature is high, gasified liquid nitrogen or the like is used to cool the Si wafers. (2) NF3 gas and NH3, H2 or N2 gas are introduced in the reaction vessel to form a reaction product, i.e., a complex(es). This reaction complex etches a native oxide film having a thickness of a few to 20 angstroms of thickness. (3) Hydrogen termination is carried out by heating in a protective atmosphere containing hydrogen. This step is carried out to decompose a complex such as (NH4)2SiF6, and cause the free arms (dangling bonds) of Si atoms to bond to hydrogen. (4) The Si wafers are moved outside the reaction vessel together with a supporting jig. (5) The Si wafers are dismounted from the supporting jig.
The reaction vessel used in the surface treating method of Patent Document 1 consists of aluminum-based material (page 7, lines 11 through 13), which had been subjected to anodic oxidation and then sealing treatment so as to provide the corrosion resistance against fluorine complexes. Since the reaction of fluorine complex stops at 60° C. or more, the temperature of a reaction vessel is desirably maintained higher than this temperature. However, when the temperature is high, since the radiation heat from the reaction vessel to a wafer disadvantageously increases, the temperature is maintained at an appropriate level. In addition, when the complexes are decomposed, the resulting Si, SiO2, SiO, SiN, SiON and the like form particles that may adhere on the wall surface of the reaction vessel. The wall temperature of the reaction vessel is maintained at 30 to 60° C., so as not to advance reaction between the adhering matters and the wall surface in the subsequent step.
Patent Document 2: Japanese Unexamined Publication of Japanese Patent Application (kokai) No. 5-275392 proposes a single-wafer treatment, in which etching gases such as NF3 and H2 are caused to flow through a conduit provided with a microwave generator and then impinge upon a wafer by down stream method. In this Patent Document, cooling gas such as nitrogen gas is caused to flow through a susceptor, thereby maintaining the temperature of a wafer to −100° C. or lower. At this temperature, the etching proportion of Si relative to SiO2 is adjusted such that the SiO2 is etched off greatly more than Si.    Patent Document 1: WO01/73832A1    Patent Document 2: Unexamined Publication of Japanese Patent Application (kokai) 5-275392    Patent Document 3: Unexamined Publication of Japanese Patent Application (kokai) 7-121124    Non-patent Document 1: J. Appl. Phys. 74(2), 15, Jul., 1993, Damage-free selective etching of Si native oxides using NH3/NF3 and SF6/H2O down flow etching page 1347, FIG. 6.